Phase 4.2: Add GridView UIDrawable type (addresses #252)

GridView is a new UIDrawable that renders a GridData object independently.
Multiple GridViews can reference the same Grid for split-screen, minimap,
or different camera/zoom perspectives on shared grid state.

- New files: UIGridView.h/cpp with full rendering pipeline (copied from
  UIGrid::render, adapted to use grid_data pointer)
- Add UIGRIDVIEW to PyObjectsEnum
- Add UIGRIDVIEW cases to all switch(derived_type()) sites:
  Animation.cpp, UICollection.cpp, UIDrawable.cpp, McRFPy_API.cpp,
  ImGuiSceneExplorer.cpp
- Python type: mcrfpy.GridView(grid=, pos=, size=, zoom=, fill_color=)
- Properties: grid, center, zoom, fill_color, texture
- Register type with metaclass for callback support

All 258 existing tests pass. New GridView test suite added.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/PyScene.cpp

@@ -4,6 +4,7 @@
 #include "PyCallable.h"
 #include "UIFrame.h"
 #include "UIGrid.h"
+#include "UIGridView.h"
 #include "McRFPy_Automation.h"  // #111 - For simulated mouse position
 #include "PythonObjectCache.h"  // #184 - For subclass callback support
 #include "McRFPy_API.h"         // For Vector type access